The present invention relates to a method and system for controlling the mixture of air and fuel supplied to internal combustion engines at a variable ratio in response to a signal derived from an exhaust gas sensor to reduce the emission of the noxious components of burnt gases.
In conventional closed loop mixture control systems, the signal derived from the exhaust gas sensor is integrated to control the mixture ratio with a time integrated gas sensor signal. The time integration provides an averaging effect on the controlled mixture ratio and serves to minimize the amount of deviation of the controlled ratio over a period of time from the desired stoichiometric point at which the harmful emissions are converted into harmless products at a maximum efficiency. However, a common problem associated with the time integrated mixture control is that the system fails to respond quickly to manual command for acceleration or deceleration. Another problem associated with the closed loop control is that the exhaust gas sensor is inactive for startup periods because of low sensor environment temperatures.